Increasing molecular weight of polyester resins having terminal hydroxyl groups

摘要

Bifunctional chain extender used in the manufacture of polyester resins having increased mol.wt.. A method for increasing the mol.wt. of polyester resins having terminal hydroxyl groups includes bringing the resin in its solid state into contact with a bifunctional chain extender having groups that react by means of addition reactions with the terminal OH grouips of the resin. The mol.wt. of polyester resins have terminal hydroxyl groups and are selected from aliphatic polyester resins obtained from 2-22C aliphatic dicarboxylic acids and 2-22C aliphatic, aromatic or cycloaliphatic diols, or 2-22C aliphatic hydroxy-acids and/or the corresponding lactones or lactides, or from aliphatic-aromatic copolyesters, polyester-amides, polyester-ether-amides, urethane polyesters and carbamide polyesters, where the repeating aliphatic unit or the aliphatic polyester sequence derives from a dicarboxylic acid or from a hydroxy-acid or lactone and lactide. The chain extender is used in a sufficient quantity to obtain an increase in mol.wt. corresponding to at least 0.1 dl/g unit of the intrinsic viscosity of the starting resin. Independent claims are also included for: (a) polyester resins selected from the above resins having an intrinsic viscosity in chloroform at 30[deg] C greater than 0.7 dl/g, substantially free of gels and obtainable using the above methods; and (b) polyester resins as above in which the ratio between the intrinsic viscosity and the melt flow index measured at 180[deg] under 5 kg of load is greater than 0.1.